The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Pumping of process fluids are used in many industries Process fluids may be pumped with a various types of pumps that are driven by a drive fluid. A slurry is one type of process fluid. Slurries are typically abrasive in nature. Slurry pumps are used in many industries to provide the slurry into the process. Sand injection for hydraulic fracturing (fracking), high pressure coal slurry pipelines, mining, mineral processing, aggregate processing, and power generation all use slurry pumps. All of these industries are extremely cost competitive. A slurry pump must be reliable and durable to reduce the amount of down time for the various processes.
Slurry pumps are subject to severe wear because of the abrasive nature of the slurry. Typically, slurry pumps display poor reliability, and therefore must be repaired or replaced often. This increases the overall process costs. It is desirable to reduce the overall process costs and increase the reliability of a slurry pump.
Direct acting liquid driven pumps have been developed, in which a high pressure drive fluid is used to pressurize a process fluid by direct contact, or separated by a membrane or piston. The known system described below is used for a slurry as the process fluid.
Referring now to FIG. 1, one example of a known slurry injection system 10 is shown. The slurry injection system 10 includes a first cylinder 12 and a second cylinder 14. The first cylinder 12 includes a slurry or process fluid inlet port 16 and a slurry or process fluid outlet port 18. The second cylinder 14 includes a slurry or process fluid inlet port 20 and a slurry or process fluid outlet port 22. The process fluid inlet ports 16, 20 are in fluid communication with a low pressure pump 24 and a process fluid tank 26. Low pressure fluid is drawn from the process fluid tank 26 by the low pressure pump 24. Process fluid is communicated through the check valves (CVs) 28, 30 in the respective process fluid inlet ports 16, 20. The check valves 28, 30 operate to allow the low pressure process fluid or slurry to be drawn into the respective cylinders 12, 14 when the pressure within the process fluid portions 32, 34 of each cylinder 12, 14, is below the check valve set pressure and prevent the pressurized process fluid from leaving the cylinders 12, 14.
Pressurized fluid from each cylinder 12, 14 is communicated through the slurry or process fluid outlet ports 18, 22 through respective check valves 36, 38. The check valves 36, 38 open when the pressure within the process portions 32, 34 is greater than the check valve set pressure. High pressure process fluid is communicated from the process fluid outlet ports 18, 22 to a high pressure process 40. The high pressure process 40 may be one of the various types of processes described above.
Each cylinder 12, 14 includes a respective piston 50, 52. The piston 50, 52 divides the respective cylinders 12, 14 into a process fluid portion 32, 34 and a drive fluid portion 54, 56.
The cylinder 12 includes a drive fluid inlet port 58 and a drive fluid outlet port 60. The cylinder 14 includes a drive fluid inlet port 62 and a drive fluid outlet port 64. Fluid is communicated from a high pressure drive fluid reservoir 66 through a three-way valve 68 to the drive inlet port 58, which is in fluid communication with the drive portion 54. High pressure drive fluid is also communicated from the three-way valve 68 to the drive fluid inlet port 62, which is in fluid communication with the drive fluid portion 56.
The drive fluid outlet ports 60, 64 are in communication with a three-way valve 70, which selectively communicates low pressure drive fluid to a low pressure reservoir 72.
Cylinder 12 has a first end 74 which corresponds to a process fluid end, and includes a proximity sensor 76. The cylinder 12 has a second end that corresponds to a drive fluid end 78. The drive fluid end 78 has a proximity sensor 80. The process fluid end 74 also includes the process fluid inlet port 16 and the process fluid outlet port 18. The drive fluid end 78 includes the drive fluid inlet port 58 and the drive fluid outlet port 60.
The cylinder 14 includes a first end 82 that corresponds to a process fluid or slurry end and includes a proximity sensor 84. The cylinder 14 includes a second end 86 that corresponds to drive fluid end. The second end 86 includes a proximity sensor 88. The proximity sensors 76, 80, 84 and 88 detect when the respective pistons 50, 52 are at the respective ends of the cylinders 12, 14.
In operation, high pressure fluid from the high pressure fluid reservoir 66 is selectively coupled to either the drive fluid portion 54 or the drive fluid portion 56, but not both. The pistons 50, 52 are preferably 180° out of phase. That is, when the piston 50 is moving left, the piston 52 is moving right, and vice versa. In FIG. 1, high pressure fluid is being communicated into the drive portion 54 so that the piston 50 is moving leftward and pressurizing the slurry or process fluid in the process portion 32. As a result, high pressure process fluid is communicated through the port 18 to the high pressure process 40. Concurrently, low pressure process fluid is being drawn into the process fluid end 34 of the cylinder 14 through the process fluid inlet port 20.
Referring now to FIGS. 2-5, an entire pumping cycle is illustrated. Specifically, FIG. 2 is the start of a pumping cycle. The piston 50 of cylinder 12 is moving toward the check valves 28 and 36. High pressure process fluid is driven toward the high pressure process 40. The piston 50 is driven by the drive fluid being communicated from the high pressure fluid reservoir 66. Piston 52 is moving toward the drive fluid end 86. That is, low pressure process fluid is communicated into the process portion 34 through the check valve 30 while the three-way valve 68 is closed relative to the fluid cylinder 14. The three-way valve 70 is opened so that drive fluid is communicated to the low pressure reservoir 72 therethrough. For cylinder 12, the check valve 68 is opened so that drive fluid is communicated through the check valve 68 into the drive fluid portion 54. The check valve 68 is closed relative to cylinder 14. Check valve 70 is closed relative to cylinder 12, but opened relative to cylinder 14.
Referring now specifically to FIG. 3, both piston 50 and piston 52 have reached respective ends of their cycles. Proximity switch 76 generates a proximity signal to halt the progress of piston 50 relative to the fluid cylinder 12. Proximity switch 88 halts the progress of piston 52 toward the drive fluid end 86 of the fluid cylinder 14. At this point, the operation of the three-way valves 68 and 70 are changed. That is, the three-way valve 68 is now switched to provide drive fluid to the drive fluid portion of the fluid cylinder 14 while the three-way valve 70 is switched to remove drive fluid from the drive portion 54 of the fluid cylinder 12. Thus, drive fluid is communicated from the high pressure fluid reservoir 66 to the fluid cylinder 14 through the three-way valve 68. Drive fluid from the fluid cylinder 12 is communicated through the three-way valve 70 to the low pressure reservoir 72. The signal from the proximity sensor 76 is used to switch the connection of low pressure fluid from fluid cylinder 12 to fluid cylinder 14. That is, low pressure fluid from the process fluid tank 26 is communicated through the pump 24 to the process fluid inlet port 16 through check valve 28. Process fluid is thus discontinued from being communicated into the slurry inlet port 20.
Referring now to FIG. 4, the pistons 50, 52 are illustrated in mid-stroke. The piston 50 is travelling toward the drive end, while piston 52 is travelling toward the process fluid end. Fluid cylinder 12 is filling with low pressure process fluid while fluid cylinder 14 is pumping high pressure process fluid to the high pressure process 40 under the control of the high pressure drive fluid being communicated through the drive inlet port 62. Drive fluid is communicated to the low pressure reservoir 72 through the drive outlet port 60.
Referring now to FIG. 5, the proximity switch 80 and the proximity switch 84 are reached, and thus the inlet and outlet port configurations are changed. That is, when the proximity switches 80 and 84 have been reached, the three-way valves 68 and 70 and the use of the inlet ports, 16 and 20 are changed to operate in the manner set forth in FIG. 2 above. This begins a new process cycle carrying forward with the examples of FIGS. 2-4.
The chart illustrated in FIG. 6 provides a summary of FIGS. 2-5. In the first row corresponding to FIG. 2, the check valve 28 is closed, while check valves 36 and 30 are open. Check valve 38 is closed. Three-way valve 68 is communicating fluid to cylinder A, while three-way valve 70 is communicating fluid from fluid cylinder 14. None of the proximity sensors has been reached. The second row of FIG. 6 corresponds to FIG. 3, in which all three of the check valves are closed. The three-way valves are in a switching state, and proximity sensors 76 and 88 have been reached.
The third row of FIG. 6 corresponds to the operation of FIG. 4, in which check valves 28 and 38 are open, while check valves 36 and 30 are closed. Three-way valve 68 is communicated fluid to fluid cylinder 14. Three-way valve 70 is removing fluid from fluid cylinder 12. None of the proximity switches has been reached.
The third row of FIG. 6 corresponds to FIG. 5, in which all three check valves are closed. The three-way valves are in a switching state, while proximity switches 76 and 84 have been reached.
There are several technological limitations set forth in the configuration shown in FIGS. 1-5 set forth above. For example, the proximity switches may not be reached at the same time by the pistons 50 and 52. This may cause the three-way valves to be switched before the other cylinder is done processing. This may result in an interruption of process fluid flow.